Stem cells are cells that have two properties consisting of pluripotency that allows production of cells that differentiate into a plurality of cells, and self-replication that allows production of cells that are identical to those cells. Stem cells derived from embryos, which are the initial development stage of a fertilized egg, are referred to as embryonic stem cells (ES cells). Although human ES cells are expected to be used in regenerative medicine, the production of new human ES cells is not allowed due to ethical considerations involving the use of fertilized eggs.
In recent years, attention has been focused on induced pluripotent stem cells (iPS cells) as cells demonstrating properties similar to those of ES cells. However, the production of iPS cells is associated with numerous problems from the viewpoints of cell malignant transformation, production efficiency and the like. On the other hand, somatic stem cells, which have the ability to differentiate into specific tissue, are not associated with ethical issues in the manner of embryonic stem cells since they are obtained from the patient's own bone marrow or other body tissue.
In the skin, epidermal stem cells (Non-Patent Document 1) are well-known to be present in the epidermal basal layer, and follicular epithelial stem cells (Non-Patent Document 2) and melanocyte stem cells (Non-Patent Document 3) have been reported to be present in regions referred to as bulge regions of hair follicles. On the other hand, although fibroblasts having a long, narrow spindle shape are present in fibrous components of the skin consisting mainly of collagen, it has not yet been determined as to whether stem cells are present in dermal fibroblasts. In addition, although skin-derived precursors (SKP) are known to exist that differentiate into a plurality of cell lines such as those of fat, glia, cartilage or muscle (Non-Patent Document 4), the correlation between dermal fibroblasts and SKP has not been determined.
Since mesenchymal stem cells, which are isolated from bone marrow as fibroblast precursors (Non-Patent Document 5), differentiate into various cells belonging to mesenchymal cell lines (including osteocytes, myocytes, chondrocytes, tendon cells and adipocytes), they are expected to be applied to regenerative medicine such as the reconstruction of bone, blood vessels and muscle. More recently, mesenchymal stem cells have been determined to have the potential of being present in numerous tissues having mesenchymal tissue, and have been isolated from fat, umbilical cord blood and the placenta (Non-Patent Documents 6 to 8). However, the presence of mesenchymal stem cells in the dermis has yet to be determined.